Patent Document 1 discloses a turbine including a housing and a turbine impeller housed in the housing. The housing has an inlet, an outlet, and a shroud surface extending between the inlet and the outlet. The turbine impeller includes a hub and a plurality of blades disposed on the outer peripheral surface of the hub. Each of the blades has a side edge extending along the shroud surface. In such a turbine, the side edge of each blade has a side-edge upstream portion disposed on the inlet side and a side-edge downstream portion disposed on the outlet side, while the shroud surface has a shroud upstream portion disposed on the inlet side and extending along the side-edge upstream portion and a shroud downstream portion disposed on the outlet side and extending along the side-edge downstream portion. Furthermore, the shroud upstream portion has an arc-shaped meridional cross-sectional shape, and the shroud downstream portion has a linear meridional cross-sectional shape along the axial direction of the hub.